An exhaust purification system for trapping particulate matter (i.e. PM) contained in the exhaust gases is mounted in an exhaust pipe of an internal combustion engine. The exhaust purification system is mounted with a particulate matter detection system having a particulate matter detection sensor. The particulate matter detection sensor detects an amount of the particulate matter contained in the exhaust gases. A fault detection of the exhaust purification system is performed based on information obtained by the particulate matter detection system.
A particulate matter detection element of the particulate matter detection sensor used for the exhaust purification system is, for example, shown in patent document 1. Electrodes having mutually different polarities are disposed adjacent to each other in the particulate matter detection element shown in patent document 1. In addition, a static electric field is formed by applying a voltage between the electrodes, and the static electric field traps the charged particulate matter. In addition, a variation of electric characteristics between the electrodes occurred by accumulating the particulate matter between the electrodes is determined. Thereby, an amount of the particulate matter is detected.
In this case, when an accumulation amount of the particulate matter is increased, electric characteristics between the electrodes do not change much. Thereby, sensor sensitivity may be reduced. Therefore, regeneration processing is performed at a predetermined timing, and the PM-trapping capability is recovered. The regeneration processing is performed by combusting the particulate matter due to heating by a heater or the like.